Devices have been proposed for exercising sphincter-type muscles. For example, Kegel in U.S. Pat. Nos. 2,507,858 and 2,541,520 employs a device having a core and a laterally extending vulcanized rubber disc which forms a stop to limit the extent of insertion. A flexible and expansible bulb surrounds the core. In use the device is inserted up to the stop and the bulb is inflated to bring its wall into engagement with the wall of the muscle of interest. A pressure guage connected to the interior of the bulb is then used to monitor compression of the bulb achieved by the efforts of the user in intentionally contracting the muscle of interest. This device has achieved a certain amount of practical use but it is not popular among users because it is uncomfortable to insert and to use and the results obtained often are not sufficiently specific to a particular muscle of interest.
Other devices for exercising sphincter-type muscles are disclosed by Hamilton in U.S. Pat. No. 3,502,328, by Buning in U.S. Pat. No. 3,598,106, by Cole in U.S. Pat. No. 3,726,273, by Harris in U.S. Pat. No. 3,752,150, by Feldzamen in U.S. Pat. No. 3,926,178, by Sasse in U.S. Pat. No. 4,048,985, by Castellana et al. in U.S. Pat. No. 4,050,449, by Remich in U.S. Pat. No. 4,167,938, by Kaiser et al. in U.S. Pat. No. 4,216,783 and by Sokol in British Pat. No. 808,867.